1. Technical Field
The present invention relates to a method of applying a coating to articles of manufacture and, more particularly, to a vapor deposition process for the application of such a coating.
2. Description of the Prior Art
In various manufacturing environments, the need may arise to apply a coating of material to a specific article of manufacture. Often, the article is extremely small, fragile, or of a shape which is difficult to coat with any degree of uniformity. In particular, many optical system applications require the use of a coated lens in the form of a spherical member. The spherical lens may be used to provide optical coupling through free space between two physically separated locations. For example, such a lens may be used between active optical device, such as a laser or LED, and an associated communication optical fiber. Conversely, a spherical lens may also be used to provide coupling between an optical fiber and a photodetector, such as a p-i-n photodiode. Regardless of the application, it is advantageous to minimize optical reflections associated with such spherical members, since reflections (at best) decrease the system coupling efficiency, and (at worst) degrade the operation of the active optical device.
In the past, spherical lenses have been coated with an anti-reflective (AR) material such as MgF.sub.2, SiO.sub.2, or other physical vapor deposited films. In particular, the spherical lenses would be loaded into a fixture and inserted in a barrel coating machine. The fixture would then be physically rotated to coat the spheres with the AR material. In order to coat both sides of the spheres, the process must be shut down and the fixture turned over. As a result, this coating process leaves a ring of uncoated surface around the middle of the device. Thus, when later utilizing the lens, orientation must be carefully controlled such that the uncoated ring portion is displaced out of the optical signal path. Another problem with the physical vapor deposition approach is the lack of uniformity of the AR coating, where this lack of uniformity affects the coupling efficiency of the lens. Further, the relatively small diameter of an individual sphere (for example, &lt;300 .mu.m) and the fragility of such a lens when fabricated out of certain materials (such as glass), results in a significant number of lenses being irreparably damaged during the coating process.
Therefore, a need remains in the art for a method of applying a uniform coating, such as an AR coating, to an article of manufacture, such as a spherical lens member.